• Nuclear Engineering and Technology
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• 제36권4호
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• pp.327-337
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• 2004

It is commonly required that tubes with defects exceeding $40\%$ of wall thickness in depth should be plugged; however, this criterion is too conservative for some locations and for some types of defects. Many studies have been done with the aim of developing an alternative plugging criteria, and these studies have shown that steam generator tubes with a certain range of axial through-wall cracks could remain in service without any safety or reliability problems. However, these studies have been limited, thus far, to consideration of single cracked tubes, necessitating a study on multiple cracks, which are commonly found. A crack coalescence model applicable to steam generator tubes with two collinear axial through-wall cracks was proposed in the previous study. In this paper, the investigation is extended to the parallel axial cracks spaced in a circumferential direction, because parallel axial cracks are more frequently detected during in-service inspections than collinear axial cracks. Interaction effects between two parallel cracks are evaluated by performing elastic and elastic-plastic finite element analyses.

• Nuclear Engineering and Technology
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• 제36권4호
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• pp.316-326
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• 2004

The $40\%$ of wall criterion, which is generally used for the plugging of steam generator tubes, is applied only to a single crack. In a previous study, a total number of 9 failure models were proposed to estimate the local failure of the ligament between cracks, and the optimum coalescence model of multiple collinear cracks was determined among these models. It is, however known that parallel axial cracks are more frequently detected than collinear axial cracks during an in-service inspection. The objective of this study is to determine the plastic collapse model that can be applied to steam generator tubes containing two parallel axial through-wall cracks. Three previously proposed local failure models were selected as the candidates. Subsequently, the interaction effects between two adjacent cracks were evaluated to screen them. Plastic collapse tests for the plate with two parallel through-wall cracks and finite element analyses were performed to determine the optimum plastic collapse model. By comparing the test results with the prediction results obtained from the candidate models, a COD base model was selected as an optimum model.

• 대한기계학회논문집A
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• 제29권5호
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• pp.754-761
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• 2005

The 40\% of wall thickness criterion which has been used as a plugging rule of steam generator tubes is applicable only to a single cracked tube. In the previous studies performed by authors, several global failure prediction models were introduced to estimate the failure loads of steam generator tubes containing two adjacent parallel axial through-wall cracks. These models were applied for thin plates with two parallel cracks and the COD base model was selected as the optimum one. The objective of this study is to verify the applicability of the proposed optimum global failure prediction model for real steam generator tubes with two parallel axial through-wall cracks. For the sake of this, a series of plastic collapse tests and finite element analyses have been carried out fur the steam generator tubes with two machined parallel axial through-wall cracks. Thereby, it was proven that the proposed optimum failure prediction model can be used as the best one to estimate the failure load quite well. Also, interaction effects between two adjacent cracks were assessed through additional finite element analyses to investigate the effect on the global failure behavior.

• 한국수자원학회논문집
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• 제57권10호
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• pp.687-697
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• 2024

실험 개수로의 유입단면에서 와, 공기방울, 소용돌이 흐름 및 과도한 유속 변동을 가능한 짧은 구간에서 효율적으로 제거하여 균일한 유속분포를 제공하는 것은 시험구간에서의 정확한 유속 측정과 흐름 현상 재현에 매우 중요하다. 이 연구에서는 과도한 유속 변동과 공기방울을 빠르게 제어함으로써 흐름 측정의 정확도를 높이기 위해 다중병렬관을 이용한 정류장치를 개발하였다. 개발한 정류장치 장치의 흐름 안정화 성능을 수리 실험을 통해 확인하였다. 다중병렬관을 이용한 정류장치는 모든 실험 조건에서 유속 변동의 지표인 난류강도를 절반 가까이 줄일 수 있는 것으로 나타났다. 직경이 20 mm이고 길이가 0.3 m인 정류관을 사용할 때 난류강도를 약 60% 이상 감소시켜 일반적인 실험수로 유입단면에서의 난류강도인 약 2.4%의 값을 유지할 수 있는 것으로 나타났다. 관의 길이가 0.3 m인 경우 난류강도의 크기는 관의 직경을 감소시킴에 따라 선형적으로 분명하게 감소하였다. 일반적인 실험실 규모 조건에서 확실한 정류 효과를 확보하기 위해서는 정류관의 직경을 20 mm로 유지하는 것이 적합한 것으로 나타났다. 고유량 조건에서 발생하는 작은 공기방울은 다중병렬관을 통과하면서 크기가 커짐에 따라 증가한 부력에 의해 약 0.24 m/s의 속도로 빠르게 수면으로 상승하여 제거 되었다. 정류장치의 공기방울 제거 성능은 정류관의 직경과 길이에 민감하지 않은 것으로 나타났다.

• 대한기계학회논문집A
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• 제29권8호
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• pp.1070-1077
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• 2005

The $40\%$ of wall thickness criterion which has been used as a plugging rule is applicable only to a single cracked steam generator tubes. In the previous studies performed by authors, several failure prediction models were introduced to estimate the plastic collapse pressures of steam generator tubes containing collinear or parallel two adjacent axial through-wall cracks. The objective of this study is to examine the failure prediction models and propose optimum ones for non-aligned two axial through-wall cracks in steam generator tubes. In order to determine the optimum ones, a series of plastic collapse tests and finite element analyses were carried out for steam generator tubes with two machined non-aligned axial through-wall cracks. Thereby, either the plastic zone contact model or COD based model was selected as the optimum one according to axial distance between two clacks. Finally, the optimum failure prediction model was used to demonstrate the conservatism of flaw characterization rules for various multiple flaws according to ASME code.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1186-1191
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• 2003

The 40% of wall criterion, which is generally used for the plugging of steam generator tubes, may be applied only to a single crack. In the previous study, a total of 9 failure models were introduced to estimate the local failure of the ligament between cracks and the optimum coalescence model of multiple collinear cracks was determined among these models. It is, however, known that parallel axial cracks are more frequently detected during an in-service inspection than collinear axial cracks. The objective of this study is to determine the plastic collapse model which can be applied to the steam generator tube containing two parallel axial through-wall cracks. Nine previously proposed local failure models were selected as the candidates. Subsequently interaction effects between two adjacent cracks were evaluated to screen them. Plastic collapse tests for the plate with two parallel through-wall cracks and finite element analyses were performed for the determination of the optimum plastic collapse model. By comparing the test results with the prediction results obtained from the candidate models, a plastic zone contact model was selected as an optimum model.

• The Plant Pathology Journal
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• 제28권4호
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• pp.401-408
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• 2012

Initial subcellular responses in susceptible (PI 274420) and resistant (cv. Hartwig) soybeans infected with the soybean cyst nematode (SCN) were examined 2 and 4 days after inoculation (DAI). Subcellular features common to both soybeans at 2 DAI included hypertrophied initial syncytial cells (ISCs) and syncytium-component cells (SCs) with a dense cytoplasm containing proliferated rough and smooth endoplasmic reticulum (RER and SER), a hypertrophied nucleolus, and reduced vacuoles, suggesting that the nematode-infected cells were dedifferentiated. In the resistant soybean, a striking initial subcellular difference from the susceptible soybean was the dilation of the RER, indicating ER dysfunction and leading to cell death. This disturbed nematode feeding, as evidenced by disrupted feeding tubes. In PI 274420, the ISC cytoplasm was depleted, with the exception of ER membranes, at 4 DAI, while the SC cytoplasm was dense with proliferation of starch-containing plastids around multiple nuclei that might be derived from the congregation of nuclei in the neighboring SCs and in part by nuclear division without cytokinesis. In cv. Hartwig, syncytia were necrotized with secondary cell wall thickening outside the plasma membrane and an extremely dense cytoplasm containing a nucleus with an electron-lucent nucleolus, accompanied by the proliferation of closely stacked parallel RER and ribosomes. These results suggest that syncytia develop continuously in PI 274420 to produce and store nutritional substances in SCs, providing for the nematode through ISC until maturation, but in cv. Hartwig, syncytia degenerate early due to excessive metabolism, blocking nematode feeding and cytoplasmic connections with adjacent intact cells.